1. Field of the Invention
The present invention relates generally to an improvement in the construction of a refrigerant compressor driven by an external drive power source, e.g., a automobile engine, and more particularly, relates to a power transmission unit accommodated in a refrigerant compressor which is suitable for being incorporated in a climate control system of an automobile so as to be driven by the engine of the automobile.
2. Description of the Related Art
There have been proposed non-clutch type refrigerant compressors driven by an external drive source without the intervention of a solenoid clutch. The non-clutch type refrigerant compressor provided with no solenoid clutch between the external drive source and the drive shaft thereof has an advantage such that when the compressor is mounted on an automobile to be accommodated in the climate control system, the driver and a fellow passenger or passengers in the automobile do not suffer from unpleasant feeling due to the shock caused by energizing and de-energizing of the solenoid clutch. Nevertheless, in the non-clutch type refrigerant compressor having no solenoid clutch between the external drive source and the drive shaft of the compressor, a change in a load torque applied to the compressor is often directly transmitted to the external drive source, i.e., to the automobile engine before the load is attenuated, and accordingly, an inconvenient change in the rotation of the automobile engine occurs.
Japanese Unexamined Utility Model Application (Kokai) No. 63-142460 discloses a transmission unit for a non-clutch type refrigerant compressor. In the transmission unit, a pulley member is mounted around a drive shaft of the compressor via an anti-friction bearing so as to receive external drive power from an external drive source. Further, a hub member is fixedly mounted on the drive shaft of the compressor so as to be coaxial with the pulley. The pulley member is operatively connected to the hub member via a plurality of pivotal drive levers to thereby transmit the external drive power to the drive shaft of the compressor via the hub member. Namely, the pulley member is provided with an annularly extending inner wall portion in which a plurality of engaging recesses are formed, and the hub member is provided with an annularly extending outer wall portion in which a plurality of similar engaging recesses are formed. Each of the plurality of pivotal drive levers is provided with engaging ends, one of which is fitted in the engaging recess of the pulley member and the other of which is fitted in the engaging recess of the hub member via an annular-shape spring member mounted around the hub member. Thus, the rotation of the pulley member can be transmitted to the drive shaft of the compressor via the pivotal drive levers, the spring member and the hub member. When a change in a load (torque) applied to the refrigerant compressor occurs, the change is reversely transmitted to the pulley member after it is attenuated by the pivotal movement of the drive levers between the pulley and hub members and the resilience of the spring member. Thus, the change in the load applied to the compressor does not adversely affect on the operation of the drive source such as an automobile engine, and accordingly a change in the rotation of the automobile engine does not occur. Further, when the change in the load applied to the compressor increases to a predetermined load level, the ends of the respective pivotal drive levers are urged to disengage from the recesses of the hub member via the annular spring member, and accordingly, an excess load torque is not transmitted to the automobile engine via the pulley member. Nevertheless, the construction of the transmission unit of Japanese Unexamined Utility Model Application (Kokai) No. 63-142460 is very complicated due to the provision of the plurality of pivotal drive levers between the pulley member and the hub member and due to the resilient support of the pivotal drive levers by the annular spring member. Further, since the number of members and parts is large and the time necessary for the assembly of the transmission unit is long, the manufacturing cost of the non-clutch type refrigerant compressor must become high.